DDT exposure more common in people with Alzheimer's: study

NEW YORK (Reuters Health) - People who had been exposed to
the pesticide DDT were more likely to have Alzheimer's disease
than those with no traces of the chemical in their blood,
researchers found in a new study.

The observation doesn't prove DDT causes Alzheimer's, or
that people who have been exposed to the chemical will develop
the degenerative brain disease, they said.

But in the complex picture of Alzheimer's - which has many
potential genetic and lifestyle contributors - this may be one
more piece to consider, according to lead author Jason
Richardson.

"If there was a single environmental factor that was
contributing to any (neurologic) diseases . . . that kind of
thing is very easy to find. That's not what we're saying here,"
said Richardson, from the Robert Wood Johnson Medical School in
Piscataway, New Jersey.

"More than likely you're looking at complex gene-environment
interactions. What we found really gives us a starting off
point," he told Reuters Health. "Now we can use that information
to try to understand who is at risk, when and ultimately, why."

DDT was banned in the U.S. in the 1970s, but is still used
in some other countries. The World Health Organization supports
using the pesticide to help eradicate malaria under certain
circumstances.

In a prior small study, Richardson and colleagues had found
levels of DDE - a broken-down form of DDT - were higher than
usual in the blood of people with Alzheimer's disease.

To learn more, they analyzed blood samples from 86 people
with Alzheimer's and 79 people without the disease.

On average, DDE levels were almost four times higher among
people with Alzheimer's than in the comparison group, the
researchers found. DDE was detected at any level in 80 percent
of people with Alzheimer's and in 70 percent of people without
Alzheimer's, according to findings published in JAMA Neurology.

A follow-up lab experiment suggested that DDE increases
levels of a protein that is known to result in the brain plaques
seen in Alzheimer's patients, Richardson said.

But that still leaves many questions unanswered, he noted.

"Obviously we want to replicate this with a much larger
number of samples and people," Richardson said.

The researchers also plan to explore DDE in other
populations, since the participants in this study were generally
patients at Alzheimer's treatment centers and their family
members.

Alzheimer's disease researcher Kathleen Hayden of Duke
University in Durham, North Carolina, said studies that measure
DDE levels in large groups of healthy people would also be
helpful. "We'd want to follow people prospectively and see
whether or not they develop dementia," Hayden, who wasn't
involved in the new study, told Reuters Health.

In an editorial, two neurologists point out there are no
data to suggest that regions of the world where people have very
high levels of DDE also have more Alzheimer's disease.

"These conclusions should be considered as preliminary until
there is independent confirmation in other populations," write
Dr. Steven T. DeKosky of the University of Virginia School of
Medicine in Charlottesville and Dr. Sam Gandy from the Mount
Sinai Alzheimer's Disease Research Center in New York.

For now, calling DDE a marker for who is at risk of
Alzheimer's is "going just a step too far," Hayden agreed.

"DDT exposure is not destiny that you're definitely going to
get Alzheimer's disease. These are things that might increase
your risk," she said.

Still, she thinks there is reason to be wary of DDT and
related pesticides.

"These agents affect the central nervous system. That's a
reason why they should be of interest to people who study
neurodegenerative diseases," Hayden said.

"For myself, I'm concerned that pesticides are used in such
abundance these days, and we don't really know what the effects
of these things are, long term."